My old Fuji Marlboro Folding bike DOES fold but going from unfolded to folding when it's about 75% folded it gets really tough and really requires some muscle. Of course when trying to unfold it also requires some muscle to get it open again. I read that some penetrating oil may do the trick but I have some questions.

1. Where do I actually put the penetrating oil? Do I lay the bike on its side and spray the PO right onto the outside of the frame onto the hinges and let it seep in to the hinges? Do I lay the bike up side down and spray directly into the frame tube where the triangular "bash guard thing" is (for the bottom hinge)?

2. Assuming the PO works and I get the frame to open and close easily again, how do I properly keep it lubricated? My understanding is that PO will not only clean out rust and gunk but will also clean out any lubricant as well. I don't want to end up back in the same place again later on.

Any help will be appreciated. Thanks.